1. Field of the Invention
The invention relates generally to the field of seismic imaging of the Earth's subsurface. More specifically, the invention relates to imaging of the Earth's subsurface using passive seismic interferometry techniques.
2. Background Art
Passive seismic emission interferometry techniques include detecting seismic signals from within the Earth's subsurface. As contrasted with conventional controlled source seismic exploration techniques (wherein a seismic source is actuated near the Earth's surface), in passive seismic interferometry, the seismic signals are generated by seismic events taking place within the Earth's subsurface. The subsurface seismic events may be naturally-occurring or may be induced by manmade activities. These seismic events may be located anywhere within the subsurface and their locations are not required to be known. The seismic signals are detected by an array of seismic sensors positioned at or near the Earth's surface generally above a volume of interest within the Earth's subsurface.
In some cases it may be undesirable to use conventional controlled source seismic techniques for evaluating the Earth's subsurface, for example, if a particular area is environmentally sensitive so as to make access and use of seismic sources unsafe or impracticable. There is a need for passive seismic methods that can make three dimensional images of the Earth's subsurface similar to those obtained using conventional controlled source seismic exploration techniques. Passive seismic methods may also substantially reduce the cost of the data acquisition for subsurface imaging.